1. Field of the Invention
The present invention relates to an electronic apparatus and, more particularly, to an electronic apparatus which has a recording device and detects the presence or absence of a recording medium at a predetermined position of a recording medium feeding path of the recording device.
2. Related Background Art
Nowadays, since recording devices are fairly miniaturized and the costs are reduced, they are equipped in various electronic apparatuses. For example, a recording mechanism is provided in an electronic desk computer, portable word processor, personal computer, electronic learning machine, electronic typewriter, etc.
The recording unit of such a kind of apparatuses or the recording mechanism of a sole recording device has a mechanism to detect the presence or absence of a recording medium such as a paper or the like at a predetermined position on a recording medium feeding path. The reason why such a detecting mechanism is provided is to control the recording position malfunction of character, image, or the like or to prevent the recording mechanism by performing the recording in the state in which no recording medium exists.
Hitherto, as a recording medium detecting mechanism in such a kind of apparatuses, a microswitch, a photosensor of the transmission type, reflection type, or the like is used.
Since the mechanical detecting means such as a microswitch or the like is operated by a recording medium which is fed, it creates an unnecessary external force that is is applied to the recording medium which is being fed. This results in a cause of the zigzag motion or jam of the recording medium.
On the other hand, since the optical detecting means such as a photosensor or the like detects in a contactless manner, such an external force is not applied to the recording medium and the feeding operation of the recording medium is not obstructed. However, there is a problem such that a malfunction occurs by the disturbed light. Hitherto, the optical detecting means is constituted in a manner such that the irradiation of the disturbed light onto the photo sensing unit of the photosensor is prevented by sealing the circumference of the photosensor or the like. However, even if the sealing property was improved, since a path to insert a recording paper from the outside of the apparatus or a path to eject the recording paper to the outside exists, it is difficult to completely eliminate the influence by the disturbed light.
The foregoing problems will now be described in detail hereinbelow by showing an example of a conventional structure.
FIG. 5 is a perspective view showing an external view of a conventional electronic apparatus. This apparatus is an electronic desk computer having an ink jet printer as a recording output device. In the diagram, reference numeral 10 denotes a main unit of the apparatus. A keyboard 14 as an input device is provided on the upper surface of the lower portion on this side of the apparatus. A printer P is provided in the rear thick portion. A display 13 consisting of a liquid crystal display, LED display, or the like is provided in the stairway portion between the printer P and the keyboard 14.
The printer P has a recording medium insertion port 11 and a recording medium ejection port 12. A recording medium such as a paper or the like is inserted from the insertion port 11. After data was recorded onto the recording medium, the recording medium is ejected from the ejection port 12 to the outside of the apparatus.
FIG. 6 shows an internal structure of the printer P of FIG. 5.
As shown in the diagram, the printer P has therein a paper feeding roller 25. A recording medium 21 inserted from the insertion port 11 passes through a paper feeding path 24 and is fed between the paper feeding roller 25 and a pinch roller 26.
The recording medium 21 is fed by the rollers 25 and 26. Data is recorded onto the recording medium 21 by a recording head 27 of the ink jet system at a predetermined position on the rectilinear feeding path near the ejection port 12. Thereafter, the recording medium is ejected from the ejection port 12.
The recording medium is detected by a photocoupler 23 at a position near the insertion port 11.
FIG. 7 shows a structure of the photocoupler 23. The photocoupler 23 has a light emitting window 31 and a photo sensing window 32.
FIG. 8 is a diagrammatical view showing the structure of the photocoupler 23 when it was seen through from the back side. A light emitting unit 33 consisting of an LED and a photo sensing unit 34 consisting of a phototransistor are provided behind the light emitting window 31 and photo sensing window 32, respectively.
The foregoing photosensor is of the reflection type. The recording medium is irradiated by the light emitting unit 33 through the light emitting window 31. The reflected light from the recording medium 21 is detected by the photo sensing unit 34 through the photo sensing window 32, thereby discriminating the presence or absence of the recording medium.
FIG. 9 shows a circuit diagram to drive and control the light emitting unit 33 and photo sensing unit 34. As shown in the diagram, a power source voltage V.sub.cc is applied through a resistor R.sub.1 to the light emitting unit 33, so that the light emitting unit 33 is lit on. The light emitting unit 33 is always lit on by the power source voltage V.sub.cc or is continuously lit on for only the period of time when it is necessary to detect the recording medium.
The emitter of the photo sensing unit 34 consisting of the photo transistor is grounded through a resistor R.sub.2 and the power source voltage V.sub.cc is applied to the collector. A medium detection signal V.sub.0 by the photo sensing unit 34 is taken out as a change in emitter potential of the photo transistor.
FIG. 11A shows a potential change of the medium detection signal V.sub.0 when the recording medium inserted into the insertion port 11 was normally detected. When the recording medium is inserted into the insertion port 11, the light emitted from the light emitting unit 33 is reflected by the recording medium and the reflected light is received by the photo sensing unit 34. Thus, the amount of conduction of the photo-transistor of the light emitting unit 33 increases and the potential of the detection signal V.sub.0 also increases. Namely, the insertion of the medium is detected by the high-level medium detection signal V.sub.0.
However, since the photocoupler 23 is disposed near the insertion port 11 of the recording medium as shown in FIG. 10, the light is irradiated onto the photo sensing unit 34 from the light emitting unit 33. The photo sensing unit 34 receives not only the signal light reflected by the recording medium but also the disturbed light which are transferred via paths such as indicated at N.sub.1 and N.sub.2.
The detection signal V.sub.0 of the recording medium which is output from the circuit of FIG. 9 is influenced by the disturbed lights In spite of the fact that the recording medium has been inserted into the insertion port 11, a detection signal indicative of the absence of the recording medium is formed. Or, on the contrary, when no recording medium is inserted, a detection signal representative of the presence of the recording medium is formed. Thus, the recording operation is disturbed. FIG. 11B shows a state in which the disturbed lights had been irradiated at a timing earlier than the timing of the insertion of the recording medium, so that a high-level detection signal indicative of the presence of the recording medium was formed in spite of the fact that the medium is not inserted yet.